Damping apparatus for a linear actuator device

ABSTRACT

A damping system used for controlling the rebound of actuator members used in high speed printers or the like is disclosed. The system involves the use of the principle that when masses collide in an elastic collision, the kinetic energy of the system remains constant. In the system, a secondary mass is free for limited movement between restraining walls at least one of which is of energy absorptive material and is positioned in the path of a rebounding actuator element. The collision between the actuator element and the mass results in a transference of kinetic energy to the secondary mass which energy is rapidly dissipated as the secondary mass collides with the energy absorptive material. Also disclosed is a holding coil for holding the actuator element following the collision with the primary mass and an intermittently operable firing coil which when energized overrides the holding force and fires the actuator element.

United States Patent Petusky 1 July 4, 1972 DAMPING APPARATUS FOR ALINEAR ACTUATOR DEVICE [72] Inventor: Neil J. Petusky, Norristown, Pa.

[.73] Assignee: Decision Data Corporation, Warminster,

[22] Filed: May 17, 1971 [21] Appl. No.: 144,084

[52] U.S. Cl. ..335/257, 335/277, 101/93 C [51] Int. Cl ..H01f 7/08 [58]Field of Search ..335/247, 248, 258, 277; 101/93 C [56] References CitedUNITED STATES PATENTS 2,625,100 l/l953 Williams et al. ..101/932,735,047 2/1956 Garner et a1. ...335/257 X 3,134,932 5/1964 Ray..335/257 Primary Examiner-George Harris Attorney--Synnestvedt & Lechner[5 7] ABSTRACT A damping system used for controlling the rebound ofactuator members used in high speed printers or the like is disclosed.The system involves the use of the principle that when masses collide inan elastic collision, the kinetic energy of the system remainsconstant-1n the system, a secondary mass is free for limited movementbetween restraining walls at least one of which is of energy absorptivematerial and is positioned in the path of a rebounding actuator element.The collision between the actuator element and the mass results in atrans-- ference of kinetic energy to the secondary mass which energy israpidly dissipated as the secondary mass collides with the energyabsorptive material. Also disclosed is a holding coil for holding theactuator element following the collision with the primary mass and anintermittently operable firing coil which when energized overrides theholding force and tires the actuator element.

15 Claims, 3 Drawing Figures Patented July 4, 1972 o BWMR 2 INVENTOR.

NEIL J. PETUSKY A TTORNE YS DAMPING APPARATUS FOR A LINEAR ACTUATODEVICE FIELD or THE INVENTION This invention relates to high speedreciprocating-actuators and while not limited, thereto is especiallydirected to an actuator used in a printer or other data recordingdevice.

BACKGROUND OF THE INVENTION which is propelled against a record mediumto effect a recording of data on the record medium. The data may berecorded in the form of a perforation caused by the movable actuatormember or in case of a printer, the actuator member typically operatesin conjunction with a rotatable print wheel carrying type representativeof data to be imprinted on the record medium. In this type of device,the record medium is locatedbetween the print wheel and actuator memberand the latter is selectively propelled so that it causes the recordmedium to impact against the print wheel thereby causing the print wheelto imprint a type character on the record medium. Immediately after theactuator member strikes the record medium it is returned to its initialposition, largely by the rebound force resulting from the impact butalso in some cases with the assistance of a spring or other returnmeans, as the actuator must be removed from the record medium rapidlyenough to prevent blurring or smearing of the characterjust printed.

Moreover the time requirements imposed are such that a cycle must becompleted in extremely short intervals, such as mil liseconds andtherefor the return portion of the cycle must be of an extremely shortduration, so that the acutator is ready to begin the next cycle as soonas possible.

As the actuator member returns to its rest position,'a large quantity ofkinetic energy is associated with it and if this energy is not rapidlyand effectively dissipated it may cause the member to bounce back andstrike the record medium a second time thereby making a second imprinton the medium. Even if the member does not strike the record medium therebound oscillations are undesirable as the member should be essentiallyat rest before the beginning of the next print cycle if the system is tohave reliability of perfonnance.

OBJECTS OF THE INVENTION With the foregoing in view, an object of theinvention is the provision of means for rapidly reducing the kineticenergy of a rebounding actuator member.

Another object of the invention is the provision of means for preventingsecondary print impressions in a high speed printing mechanism.

A more specific object of the invention is the provision of apparatususing momentum effects for transferring energy between masses anddissipative collisions for dissipating the kinetic energy transferred.

In summary, the foregoing and various other objects of the invention areachieved by the provision of a secondary mass positioned in the reboundpath of the actuator member so that the actuator member collides withthe secondary mass in an elastic collision. The invention takesadvantage of the principle that in an elastic collision between twomasses the kinetic energy of the system remains constant. According tothe invention the secondary mass collides with a restraining wallfollowing its initial collision with the rebounding actuator member.Restraining walls are positioned on both sides of the secondary mass andone or both of the restraining walls are formed of a material which ishighly energy absorptive. Thus, it can be appreciated that when theactuator member strikes the secondary mass a quantum of its energy canbe transferred to the secondary mass and that as the ratio of the massesapproaches unity virtually all of the energy can be transferred. If thesecondary mass is slightly heavier than the actuator point of impact ofand the secondary mass will move at a relatively large velocity in thesame direction as the actuator member was moving just prior to the timeof collision. Since the secondary mass is confined by the two walls, italmost immediately collides with the first of these walls and if thatwall is made of energy absorptive material it'loses a large portion ofthe kinetic energy to that wall. According to the preferred embodimentof the invention when the secondary mass rebounds from the energyabsorptive wall it almost immediately impacts on the other wall and ifthat wall is also of an energy absorptive material it loses a largepercentage of the remaining kinetic energy. Collisions of the secondarymass with the two walls'will continue until all of the kinetic energy inthe secondary mass is dissipated. Because of the proximity of the wallsrelative to the secondary mass, the kinetic energy in the secon darymass is dissipated in a relatively short period of time, i.e., beforethe actuator member strikes it a second time. should there be suflicientkinetic energy remaining in the actuator biasing it towards thesecondary mass. The holding coil may 4 be constantly energized and afiring coil which is not normally energized may provide an impellingforce on the actuator member which is greater than the holding force inorder to propel the actuator member. The motion of the actuator elementis typically rectilinear but actuators incorporating the principles ofthe invention need not follow straight line paths and may move inarcuate or other paths.

Turning to the illustrative embodiment of the invention reference willbe made to the drawings in which:

FIG. 1 is a plan sectional view of a preferred embodiment of theinvention;

FIG. 2 is an enlarged view of a portion of the invention of FIG. 1; and,

FIG. 3 is a graphical representation showing mass and energyrelationships involved underlying the invention.

Referring now to FIGS. 1 and 2, in the illustrative embodiment of theinvention, the actuator device comprises a block 10 in which is mounteda coil assembly 11. Coil assembly 11 comprises a tube or core 12 formedof a non-magnetic material such as glass. Pole pieces l3, l4 and 15 aremounted on the tube 12. A firing coil 16 is provided intermediate polesl4 and 13 and a holding coil 17 having a relatively small number ofampere turns with respect to the ampere turns of the firing coil 16 isprovided between pole pieces 14 and 15. Leads 18 are provided forenergizing the coil 16 and leads 19 are provided for energizing the coil17.

Mounted within the tube 12 is the actuator member or slug element 20which in the preferred embodiment of the invention is formed of asubstantially non-compressible magnetic material. Preferably the slugelement 20 is held in position by the holding coil 17 and to this endmeans are provided for energizing the holding coil. Holding coil 17applies a holding force on the element which in the absence of a greaterforce applied by the firing coil is sufficient to ordinarily hold itagainst movement.

Upon energization of the selectively operable firing coil 16, a force isapplied axially of the tubel2 which is sufliciently great to overcomethe holding force and propel the element 20 from the tube. In the caseof a printer, the-element 20 is propelled against the record mediumwhich may be a punch card, paper tape or the like with sufiicient forceso that is impacts on the record medium thereby forcing it against aprinting wheel and effecting a printing operation.

Following the printing stroke of the element, it is returned to itsinitial position of rest shown in FIGS. 1 and 2. In the case of a highspeed printer wherein the slug element acts as a hammer forcing therecord medium against an element bearing type characters, the element ispossessed of sufficient member the actuator member will rebound slightlyfrom the kinetic energy to rebound rapidly away from its position atimpact and to move with high velocity towards its initial position. Insome systems, however spring means or some other means providing anassisting force may be provided to assist in the return of the actuatorelement to its initial position.

In either event, the invention is intended to damp the high quantity ofkinetic energy which the element 20 may possess during its return orrebound movement. In order to dampen the rebound movement so as toprevent the element from again striking the record medium, the inventioninvolves the use of a secondary mass or energy transfer element 22located so that it is in axial alignment with the element 20 in positionso that the element 20 collides with it during its return movement.Element 22 is preferably formed of a non-compressible material and ismounted between a pair of walls 23 and 24.

Each of walls 23 and 24 is positioned in proximity to the mass 22. Atleast one of the walls is formed of an energy absorptive material. Anexample of an energy absorptive material producing excellent results isa high density polymer sold under the trademark GAR-DUR by Garland Mfg.C0,, Soco, Maine. According to the literature GAR-DUR is an ultra highmolecular weight polyethylene.

As noted above the collision between the actuator element and the energytransfer element is theoretically an elastic collision althoughperfectly elastic collisions are unknown except perhaps between atoms,molecules and electrons. For the purposes of this invention however, itis contemplated that substantially any materials may be employed for theactuator element and the energy transfer element which do notsubstantially compress when they collide under the conditions of usecontemplated. The suitability of the materials to be employed may bereadily determined by a few field trials.

Attention is now directed to FIG. 3 which illustrates th mass and energyrelationships involved in the invention. The curves in FIG. 3 representthe case where a collision has occurred. The curves E and V indicate thekinetic energy and velocity of the first mass that is, of the actuatoror slug element 20. Curves E and V indicate the energy and velocity ofthe secondary mass or energy transfer element 22. It can be seen fromFIG. 3 that as the ratio K of the two masses approaches unity, theenergy and velocity of mass I that is, the actuator element 20, drop to0. Where K is between about 0.5 and about 2, substantial energy transfercan be achieved.

In devices of the kind illustrated, best results are obtained when K isslightly greater than unity. In that case, as shown in FIG. 3, thevelocity of element 20 is negative following the collision so thatelement 20 rebounds slightly following the collision. The significanceof this is that the two elements separate more rapidly for a giventransfer of energy during the time that the secondary mass is vibratingoff the two walls 23 and 24. Because of this, the energy of thesecondary mass is not retransferred to the primary mass in an elasticcollision before its energy is absorbed by the energy absorbingmaterial. In actual practice, best results are achieved when the ratioof the masses is between L2 and 1.5 but these values may vary somewhatdepending on the materials actually employed.

As explained above holding coil 17 biases the actuator element towardsits original point of impact and it should be sufficient to constrainthe actuator element within the tube from excessive movement when itrebounds from the energy transfer element or secondary mass. Desirably,the coil biasing force should be just sufficient to return the actuatorelement to its point of impact with the energy transfer element at aboutthe time that the energy transfer element has transferred all of itsenergy to the energy absorptive material.

In most instances it has been found that there is so little kineticenergy remaining in the actuator 20 that it may be considered to be atrest for engineering purposes following the first or second collisionwith the energy transfer element and it has been found that in actualtrials in printers and punches wherein the cycle time is about 5milliseconds that this is the case. In some instances however, severalcollisions between the actual element and the transfer element can takeplace but these collisions occur at an ever increasing rate with everdecreasing residual energy so that the time for the actuator element tocome to rest is quite short.

I claim:

1. Apparatus for damping the rebound oscillations of a firstreciprocating element used in the recording of data on a record medium,said apparatus comprising a secondary .element located in the reboundpath of the first element for collision with said first element duringits rebound motion, wherein the ratio of the mass'of said secondaryelement to said first element approaches unity, said secondary elementbeing mounted for limited movement in the direction of motion of thereciprocating element following a collision therewith and a body ofenergy absorptive material for limiting movement of the secondary mass.

2. Apparatus according to claim 1 wherein the ratio. of masses of thesecondary element relative to the first element is greater than I.

3. Apparatus according to claim 2 wherein the ratio of the masses of thesecondary element relative to the first element is between about 1.2'and1.5.

4. Apparatus according to claim 1 wherein the length of the path ofmovement of. the reciprocating element is long relatively to the lengthof path of movement of the secondary element.

5. Apparatus for damping the rebound oscillations of a linear actuatorelement used in the recording of data on a record medium comprisingintermittently operable firing force applying means for propelling saidelement towards the record medium, an energy transfer member in therebound path of said actuator element for collision with the actuationelement during its rebound motion, said energy transfer member beingmounted for limited movement along the path of movement of the actuatorelement upon a collision with the actuator member, said member and saidelement being formed of a relatively non-compressible material and anenergy absorptive material positioned in the path of movement of saidenergy transfer member for absorbing the kinetic energy of said energytransfer member upon a collision therewith.

6. Apparatus according to claim 5 comprising holding force applyingmeans for holding said actuator member following rebound from saidenergy transfer member.

7. Apparatus according to claim 6 wherein said holding force meansapplies said holding force at a value which is small relative to saidfiring force.

8. Apparatus according to claim 5 wherein said actuator member is formedof a magnetic material, said firing force means comprising a coilsurrounding said actuator member and energizable to propel said actuatormember in a first direction, and wherein the number of ampere turns ofthe holding coil is relatively small with respect to the ampere turns ofsaid firing coil.

9. Apparatus according to claim 5 wherein the ratio of the mass of theactuator element to the energy transfer element is between about 1.2 andabout 1.5.

10. Apparatus for damping the rebound oscillations of a slug elementused for high speed printing or the like comprising firing forceapplying means for driving the element against a record medium, anenergy transfer element located in the rebound path of said slugelement, said energy transfer element having a surface against whichsaid slug element impacts when it rebounds from the surface of saidrecord medium and being mounted for movement in response to the impactwith the slug element, and an energy absorptive element on at least oneside of said energy transfer element in the path of movement of theenergy transfer element and positioned for collision therewith, saidenergy absorptive element being adapted to absorb the energy of saidtransfer element during rebound oscillationsof said element.

11. Apparatus according to claim 10 wherein an energy absorbing elementis mounted on both sides of the energy transfer element.

12. Apparatus for damping the rebound oscillations of a slug elementfollowing the firing of the element towards a 13. Apparatus according toclaim 12 wherein both of said secondary impact members are formed of anenergy absorptive material.

14. Apparatus according to claim 13 wherein the said energy transferelement is heavier than the slug element.

15. Apparatus according to claim. 14 wherein the ratio of the weight ofthe energy transfer element to the weight of the slug element is about1.2 to about l.5.

1. Apparatus for damping the rebound oscillations of a firstreciprocating element used in the recording of data on a record medium,said apparatus comprising a secondary element located in the reboundpath of the first element for collision with said first element duringits rebound motion, wherein the ratio of the mass of said secondaryelement to said first element approaches unity, said secondary elementbeing mounted for limited movement in the direction of motion of thereciprocating element following a collision therewith and a body ofenergy absorptive material for limiting movement of the secondary mass.2. Apparatus according to claim 1 wherein the ratio of masses of thesecondary element relative to the first element is greater than
 1. 3.Apparatus according to claim 2 wherein the ratio of the masses of thesecondary element relative to the first element is between about 1.2 and1.5.
 4. Apparatus according to claim 1 wherein the length of the path ofmovement of the reciprocating element is long relatively to the lengthof path of movement of the secondary element.
 5. Apparatus for dampingthe rebound oscillations of a linear actuator element used in therecording of data on a record medium comprising intermittently operablefiring force applying means for propelling said element towards therecord medium, an energy transfer member in the rebound path of saidactuator element for collision with the actuation element during itsrebound motion, said energy transfer member being mounted for limitedmovement along the path of movement of the actuator element upon acollision with the actuator member, said member and said element beingformed of a relatively non-compressible material and an energyabsorptive material positioned in the path of movement of saId energytransfer member for absorbing the kinetic energy of said energy transfermember upon a collision therewith.
 6. Apparatus according to claim 5comprising holding force applying means for holding said actuator memberfollowing rebound from said energy transfer member.
 7. Apparatusaccording to claim 6 wherein said holding force means applies saidholding force at a value which is small relative to said firing force.8. Apparatus according to claim 5 wherein said actuator member is formedof a magnetic material, said firing force means comprising a coilsurrounding said actuator member and energizable to propel said actuatormember in a first direction, and wherein the number of ampere turns ofthe holding coil is relatively small with respect to the ampere turns ofsaid firing coil.
 9. Apparatus according to claim 5 wherein the ratio ofthe mass of the actuator element to the energy transfer element isbetween about 1.2 and about 1.5.
 10. Apparatus for damping the reboundoscillations of a slug element used for high speed printing or the likecomprising firing force applying means for driving the element against arecord medium, an energy transfer element located in the rebound path ofsaid slug element, said energy transfer element having a surface againstwhich said slug element impacts when it rebounds from the surface ofsaid record medium and being mounted for movement in response to theimpact with the slug element, and an energy absorptive element on atleast one side of said energy transfer element in the path of movementof the energy transfer element and positioned for collision therewith,said energy absorptive element being adapted to absorb the energy ofsaid transfer element during rebound oscillations of said element. 11.Apparatus according to claim 10 wherein an energy absorbing element ismounted on both sides of the energy transfer element.
 12. Apparatus fordamping the rebound oscillations of a slug element following the firingof the element towards a reaction surface comprising an energy transferelement located in the rebound path of said slug element, said energytransfer element being movable upon collision occurring during therebounding of said slug element to thereby transfer kinetic energy fromsaid slug element, secondary impact members located on either side ofsaid transfer element in proximity thereto, at least one of said membersbeing formed of an energy absorbing material for absorbing the kineticenergy imparted by said slug element to said transfer element. 13.Apparatus according to claim 12 wherein both of said secondary impactmembers are formed of an energy absorptive material.
 14. Apparatusaccording to claim 13 wherein the said energy transfer element isheavier than the slug element.
 15. Apparatus according to claim 14wherein the ratio of the weight of the energy transfer element to theweight of the slug element is about 1.2 to about 1.5.